Automation for the assembly of optoelectronic or photonics devices is an important way to reduce the manufacturing cost of these products. In one such manufacturing process, an optical axis of an optoelectronic device (for example, a light emitting device, photodetector or optical waveguide) is aligned with an optical axis of an optical fiber, and the aligned parts are then mechanically coupled. If the optical coupling efficiency is low, problems like a high loss of optical energy, a short transmission distance and a low signal-to-noise ratio may result.
Thus, high-precision alignment techniques are adopted in the assembly of these products to ensure high performance of the products. Both active and passive alignment techniques have been developed to address the requirement of high coupling efficiency. There are advantages and disadvantages associated with each of these techniques. Generally speaking, passive alignment techniques are faster but ultimately, the precision achieved using these techniques can hardly be less than one micron. In addition, the initial cost for making submounts for performing passive alignment is high. In comparison, with current motion control technology, active alignment techniques can achieve sub-micron accuracy and no passive alignment submount is needed. Unfortunately, most of the active alignment techniques are very time-consuming and therefore also very expensive for manufacturers.
Single-mode pigtailed laser diode devices are among the most common optoelectronic components which are produced in large quantities. A process for manufacturing these devices includes an alignment and coupling process as described above. Despite the simple structure of this device, its manufacturing cost is quite high due to the fact that it may incur a long assembly process time to align a single-mode fiber with a laser diode source actively in order to obtain a product with reasonably high coupling output. As a matter of fact, some manufacturers still rely on manual or semi-automated systems to perform this active alignment in their production lines. In order to reduce the manufacturing cost of this kind of products, a fully-automated system with a short assembly process cycle and high processing yield is needed.
Various techniques have been developed to speed up the active alignment process and to reduce the time needed for obtaining a high coupling efficiency from a laser diode source to a single-mode optical fiber. In U.S. Pat. No. 6,325,551 entitled “Method and Apparatus for Optically Aligning Fibers with Optical Devices”, an active alignment technique makes use of a positioning system with a high frequency closed loop optical feedback of a modulated signal to and from a light emitting device under assembly. The technique as described in this US patent imposes some complications on the electronic design and motion control for the system design.
Another prior art is described in U.S. Pat. No. 5,666,450, which describes an infrared position sensitive device (PSD) using InGaAs sensing elements to perform a so-called ‘dark search’ or ‘rough search’ of a laser spot before conducting a fine alignment search. This process seeks to reduce the overall alignment process time by dividing the two searches. However, a lot of the process time is still spent on the fine alignment process. The implementation of the technique as described in this US patent is also not easy since the high resolution InGaAs infrared two-dimensional PSD used with the apparatus is very expensive and is not readily available commercially.
The current invention has been especially developed to address the need of assembly automation and the reduction of the alignment process time for these fiber pigtailed devices, although it is also suitable for the coupling of other optoelectronic devices.